IBM Power System 9040-MR9 Manual page 52

Figure 38. Releasing the system processor module from the tool
j) Repeat steps "18.a" on page 33 through "18.i" on page 37 to remove all of the system processor
modules.
19. Remove the power midplane.
a) Unplug the cable from its connector on the power midplane.
38 Power Systems: System backplane